1986 carb to TPI conversion. ECM - 7165. I don't remember the MEMCAL ID but when I looked up a list of MEMCALs (or PROMs as the terms seem to be bandied about interchangeably) for 86 my number was in the list.

The car acts like it wants to start but won't. I suspect the cold-start injector is doing its thing but the other injectors aren't.

The harness and ECM came from an '86 TPI setup I purchased on Ebay. The harness was in good condition. I have not replaced the injectors that came with the intake.

I have checked and verified the following:

All injector coils measure over 20 ohms.
All solenoid coils measure over 10 ohms.
Fuel pressure is at 60 psi (I know, I need to adjust the regulator down some)
With A-B shorted, the SES flashes code 12 but no other codes.
When the key is first turned on, the SES light winks and then is on steady (I bypassed the light control module that the carb'd car uses and wired straight to the ECM. Yes, I can read schematics; I used to be an electronic technician)
I have spark.
The injector circuit is not shorted to ground (checked wih ECM unplugged)
The green and blue injector wires are on D15 & D16 per schematic.
I have tried three different remanuifactured ECMs and one I pulled from the boneyard. The only common element is the MEMCAL.
When I check the injector power while cranking the engine, my test light (12 v) to ground is on steady and does not flash (yes, I am checking the ECM side and not the the 12v side).

Can a bad MEMCAL pass the checksum and still cause a no-start condition? The limp mode doesn't seem to work either as the car still doesn't start when I disconnect the MAF sensor.

What am I missing? I've been two weeks trying to get this thing started and I am really flustered at this point. Does anybody have any insight or suggestions as to what to try next?

Thanks in advance...

 

The '89 MEMCALs had VATS enabled. That will prevent the injectors from firing. If you can post the BCC (3 or 4 letter code on the PROM) I can check if it is from an '89.

Other then that, the ECM needs to receive DRPs in order to fire the injectors. You can have spark but the DRP to the ECM is still bad. During crank the ignition module runs on it own. No signal from the ECM is required.

So a bad ignition module can also cause a 'no injector firing' action. Yet still spark the plugs.

Note that the MAF sensor isn't used during cranking. And even if disconnected while the engine is running will not put the ECM into limp mode. To try limp mode pull the EPROM out of the MEMCAL.

RBob.

 

Thanks for the reply!

I will pick up a new ignition module today as the spark I noted was weak compared to the spark on my '78 El Camino HEI. I will post the BCC info tonight from home as well as the results from the new ignition module installation.

I did not realize the crank portion of the startup was independent of the ECM. Thanks for that info. I have tried to be conscientious and do my research before posting questions so your input is greatly appreciated!

 

Ok.

I installed an Accel ignition module and MSD coil. No change to the previously mentioned symptoms.

The PROM is identified as AUM 3236. According to a list I spotted somewhere on the web, this is applicable to the '86 5.0 DFI 305. However, I wouild place greater confidence in confirmation or denial in this forum. If I have to get a new PROM, I was planning on picking up Hypertech Thermomaster, although I believe I will have to order it unless I can find one in Orange County (Ca.).

Could the ESC module have a problem? It is about the only thing I have not replaced at this point.

Thanks again for your input!

 

The AUM is for an '86, so no VATs with it. I doubt the ESC module would cause the injectors to not fire. It only signals the ECM that knock is present, which during cranking the ECM doesn't even check for.

It may be that the ECM is bad and not firing the injectors. Note that the ECM needs to see DRPs in order to fire the injectors. Easy test for this is: key-on, engine-off. Wait for fuel pump to stop running (about 2 seconds). Then give the engine a brief crank and leave the key in the on position.

Did the fuel pump start running again? It should for 2 seconds then stop. Can tap the starter to check again. If the fuel pump does kick on for 2 sec's at each crank then the ECM is getting DRP's.

I also noted this in the first post: All injector coils measure over 20 ohms.

The injectors should ohm out to 14 - 16 ohms. If over 20 then something is wrong with them.

RBob.

 

Ok.

A little more definition...You are right, the injector coils run about 16 ohms each. I mispoke previously.

Yes, the fuel pump comes back on after a brief crank for a couple of seconds.

Should my 12v test light just wink or should I be able to discern distinct on and off states of the lamp when cranking the engine and looking at the ECM side of the injector wiring? At low rpm I was expecting distinct states but since your test of the fuel pump indicates DRP, then maybe I am not interpreting the test light indication correctly.

Short of tearing the fuel rail off, is there any way I can verify the injectors are working? Could sitting dry for an extended period of time cause the poppet valves to stick closed?

Another question that has me bugged...is the timing pointer in the same general location as other small block Chevy's? The pointer on mine is missing and I assumed the pointer was in the same basic location. And is the balancer rubber-isolated from the hub? When I bring #1 up to what should be TDC, the timing mark on the balancer is at about 12:00. I would expect it to be further down, say about 2:00 if the pointer is in the same location. Maybe my problem has been timing. How sensitive is a TPI engine to static timing?

Thanks,

 

just a random thought because i spent literally months chasing an intermittent injectors not firing issue.

Theres a wire that goes from the icm to the ecm that gives pulse reference. No reference and the injectors wont fire.

 

if the ECM fires the injectors, you would be able to see the test light flash. see the test below for bulbs that work better than a test light.
yes, the injectors could be stuck closed from sitting up. most of mine were stuck after sitting for a few months.
you may have a balancer from a pickup, with the truck balancers at TDC the timing mark is around the 12 o'clock position.

check the TPS voltage, if its too high you could be in clear flood mode.
if your still not getting the injectors to fire, here is another test for you to do.
this is from memory, so there is 1 part im not certain of.

for this test unplug all the injectors so you don't dump liquid fuel in the motor or damage the injectors.
unplug the 4 way connector going to the distributor.
hook up a noid light or a test light to one or more of the injector connectors. if you don't have any noid lights or an extra test light, a light bulb or 2 for the instrument
cluster will work fine & are cheap, i believe they are #194.
now turn the key on & with a test light check for power at the injector connectors.
did you have power? yes? good.
here is part of why you unplugged all the injectors, now you want to ground the ECM side of one of the injector connectors & watch the light(s) you plugged into the injector connectors & see if the bulbs light up. if they did your ready to see if the ECM is able to fire the injectors.

this next part is what i don't remember for certain, the test light may need to be hooked to ground instead of positive, but i believe it is positive.
don't worry, if you do it the wrong way using a test light it won't hurt anything.
now with your regular test light hooked to battery positive, find the purple/white tracer wire in the 4 way distributor connector, i believe its B in the connector, this is the wire Doug is talking about. now touch the probe of your test light to it. you don't need to make solid contact, moving the probe from side to side to make & break contact works great.
did the lights you put in the injector connectors flash? if they did the ECM isn't seeing pulses from the distributor. check the wiring from the 4 way connector to the distributor, lastly recheck the module.
if the lights didn't flash, check the purple/white tracer wire from the 4 way distributor connector to the ECM. if it checks good, recheck all of your powers & grounds to the ECM. if they check good, try a known good ECM.

 

Have you tried just spraying a little starting fluid into the throttle body to see if it fires on that? then start hunting from there.

 

If the injectors are stuck closed, the only way to unseat the valves is to do an off-the-car cleaning, correct? Is there any specific procedure I can use? The references I read on-line indicate using pressurized equipment to unstick the valves and that would entail a fixture of some type.

I will double-check the wiring when I get home tonight (I'm at work right now). Can somebody let me know about the timing scale? I've asked the car's original owner about the harmonic balancer to find out if it has been replaced.

Thanks so much for all of the responses. I will continue to post as my troubleshooting progresses and I hopefully find a resolution.

 

It would need to be hooked-up to the Schrader valve which is on passenger side rear corner of the fuel rail

 

I don't think pressurizing the fuel rail will free stuck poppet valves. The injectors need to be reverse-pressurized to free the valves which is where a fixture is needed to secure the injector so it can be pressurized from the nozzle side. I could bring each cylinder up on TDC and pressurize the cylinder but I don't know about the possibility of damage to the piston rings. I would only be able to pressurize up to the limit of the cylinder's ability to hold compression (which should be between 110-140 lbs but would that be enough to free a stuck poppet?).

I still need an answer to the timing scale (tab) question. Is it in the same location as a 350?

Thanks again for all the responses!

 

Well,

I picked up some parts at Harbor Freight and with the line from my compression gauge made myself a gizmo to pressurize the cylinders and hopefully pop the injector poppet valves free. At 130 lbs. I just about broke my wrist and arm using an 18 in. breaker bar to hold the crank in place while pressure built up. The #1 injector valve popped loose but #3 refused to budge. At this point, my phantom electrical problem my have been a mechanical problem all along. The injectors sat for 18 months on my workbench and who knows how long it sat before that.

I've ordered a new set of Accel injectors and they hopefully will come in by the middle of next week. I will post the results of my injector replacement after I get them installed.

 

It's alive!

Three weeks chasing an "electrical problem" and it was the injectors. Ordered a set of Accel injectors and finally got them installed last night and the whole thing put back together. After a little bit of adjustment of the timing, it fired right up. Now I just have to replace the plugs tonight and check the ALDL data to see how it is running.

I used 26 lb. injectors based on future installation of World heads, a lumpier cam and Edelbrock TES. Also, TPIS is going to be releasing a MiniRam manifold with EGR provision. They said they are not going to get it certified but I am going to check with a CARB referree to see if I can get it bought off since the rest of the engine will retain all of the sensors.

While the whole thing was apart, I also took out the ribs in the upper plenum, installed an air foil in the throttle body, an aluminum driveshaft, polyurethane torque arm and trans mounts and a disc brake rear axle.

Will update my progress after I get a test drive completed.

 

not going to read the whole thing again but out of curiosity did you ever check the resistance on the actual injectors?

i spent a couple months chasing a dropped cylinder, 3 shops and a bunch of wasted time/money later, finally did that myself and realized it was a dead injector

 

The injector coils all tested good but when I removed them from the engine I found broken caps on half of them. That plus the fact I couldn't get #3 to open when reverse-pressurizing the cylinder made me replace the set.

Now I have a different problem. I finally got the car started but it won't idle below 1700, above half-throttle I've got nothing and it throws code 33. I'm pretty sure my IAC is either stuck or not operating smoothly causing the idle problem but the code 33 has me a little bit baffled. I need to run through the MAF sensor troubleshooting chart and make sure my MAF is good. I changed it out with another one but the code 33 is still there. Do I have to clear the codes after component change-out or will the ECM just recognize a change and drop the code?

I have WinALDL and their cable but I can't get any data from the ECM. I checked the wiring and in this car I replaced the carb with TPI so I had to add the wire from ALDL pin E back to the IP to TPI connector. All of the other wires basically were there. Still no data. I was hoping the ALDL data would give me some better info to help zero in on the problems.

My question is has anybody done the carb to TPI conversion and if so, what other wiring changes had to be made to get ECM data output? I've checked the wiring against the '86 assembly manual wiring diagrams and it looks like everything is correct. I have tried both 10K and short across ALDL A-B but still no data.

I'm going to check the TPS output tomorrow. I found the adjustment procedure for the IAC, but how do you test the IAC?

 

Ok, so I I followed the procedure in the tech article for TPS and IAC. When I unplugged the IAC the motor idled right down to about 450 with no adjustment. When I cleared the computer error codes and hooked the IAC up, the idle went back to being unstable. I would presume this indicates a bad IAC.

I test drove the car and it did not throw any error codes but I have nothing above half-throttle. What's up with that?

I will try to check the TPI harness wiring back to the ALDL tomorrow and make sure Pin E on the ALDL is hooked up to serial out from the ECM. I really need to get WinALDL working so I can see what is happening.

Any comments?